PS CS5 From Windows to Mac?

Hello denisem62721688! If you have CS5 License for Windows, you might be able to upgrade it for a Mac version, but I'm not sure, you can see more here Exchange a product for a different language or platform version . But the best thing is to see if you can still buy/upgrade the license, it's better to Contact Customer Care

Exchanges are only available for the current version. So they are discontinued, since Creative Cloud has free platform swaps.

I doubt you'll get much for it. It's not upgradeable, and pretty soon (if not already) it will stop working on new OSes. In fact it most likely wouldn't have worked on your new iMac even if you could get the switch.

Software doesn't age with grace. It relies on a whole ecosystem that has kept moving on. If you want to use old software like CS5, you really need to deep-freeze your whole system at that point in time.

Aside from that, you need to fill out a transfer of ownership and send that to Adobe, to keep the license legal for the new user.